Seed germination and seedling survival of Drosera rotundifolia (L.) cultivated on Sphagnum: Influence of cultivation methods and conditions, seed density, Sphagnum species and vascular plant cover

Round-leaved sundew (Drosera rotundifolia L.) is a rare bog species that is commonly collected for the European herbal market in the wild, leading to the destruction of its natural populations. The aim of this study is to compare sundew cultivation methods on Sphagnum lawn that meet the requirements of the pharmaceutical industry and could promote a sustainable commercial cultivation. Seed germination and seedling survival of D. rotundifolia were studied in biodegradable cellulose pots, paper mesh bags or directly sown (cultivation methods) in a natural, a semi-natural Sphagnum farming and a greenhouse environment (cultivation conditions); using different seed densities. Drosera was cultivated on Sphagnum palustre or S. papillosum lawn and with or without co-occurring vascular plants. Best seed germination for all cultivation methods was recorded in the greenhouse, most successful were cellulose pots (≤ 26 %). Cellulose pots were also most successful under semi-natural (≤ 15 %) and natural (≤ 7 %) conditions. Lowest seed germination rates (< 1 %) were found for direct sowing under semi-natural and natural conditions, indicating that large-scale cultivation by direct sowing requires large quantities of seeds. High survival rates were observed for all cultivation methods in the second year of growth (mean 70 %). The removal of co-occurring vascular plants showed a positive correlation with the number of Drosera seedlings in the first year and led to a higher number of surviving Drosera plants in the second year. Cultivation of D. rotundifolia in biodegradable cellulose pots and direct seed sowing on Sphagnum lawns meet the cultivation requirements of the pharmaceutical industry and have many ecological benefits compared to collection in the wild.